Algorithms, Captions, And Labels: A Guide To Robust Cross-Referencing In Latex

Defining Labels for Cross-Referencing

Labels act as targets for cross-references in LaTeX documents. By assigning unique identifiers to sections, figures, tables, algorithms, and other document elements, you enable precise linking between related content.

The \label command defines labels in LaTeX. When placed inside a sectioning command, figure environment, caption, algorithm block, or other content container, the \label creates an anchor that can be cross-referenced from anywhere in the document.

Best Practices for Defining Labels

Use descriptive names - \label{sec:literature_review}
Keep names consistent across similar objects - fig:heatmap_1, fig:heatmap_2
Differentiate between labels for unique objects
Place labels after captions or section titles

Following naming conventions for labels improves maintainability. If labels relate clearly to their associated content, references will remain valid despite document edits.

Table of Contents

Referring to Labels for Cross-Referencing

The \ref command generates links to labeled document elements in LaTeX. It outputs formatted references based on the type of label,replacing the label name with an appropriate representation like a numeral, title, or page number.

Customizing Cross-Reference Text

Formatting options can tailor reference text to suit readability needs:

\ref{label} - Default formatted cross-reference
\ref*{label} - Only the label name appears
\autoref{label} - Reference with contextual hyperlink text
\nameref{label} - The title or caption text is output

For example, \autoref{} can output "Figure 1.2" linking to the associated figure, while \nameref{} prints the full figure title or caption text.

Tables, Figures, and Automatic Numbering

LaTeX handles numbering, titling, and cross-referencing for common floating document elements like figures and tables out-of-the-box:

Table and figure counters track numbers
Captions embed content details
Labels link to genereated numbers and titles

For example:


\begin{figure}
  \centering
  \includegraphics[width=\linewidth]{result.png}
  \caption{Performance results. \label{fig:results}}  
\end{figure}

Enables referencing "Figure \ref{fig:results}" with output like "Figure 1.2". The figure counter handles numbering while the caption label establishes a link target.

Customizing Float Label Types

The \captionsetup command tailors how captions and their labels are rendered in floats:

labelformat - Format label text ({name}, numcount, title)
labelsep - Separator between number and title
labelfont - Text style for labels


\captionsetup{
  labelfont={bf},
  labelformat={drop},
  labelsep=newline,
}

This omits the default "Figure 1.2: " caption label, keeping only the bold title text for conciseness.

Troubleshooting Cross-Referencing Issues

Link errors or incorrect references are common LaTeX issues:

Undefined control sequence - Undefined label
Missing number/name inserted - Broken label link
Incorrect caption/number reference - Outdated label

Debugging Faulty Label References

Debugging techniques to resolve reference errors include:

Commenting \ref to locate undefined labels
Printing \getrefnumber{} to check target numbers
Tracing \label and \ref locations interactively
Checking auxiliary .aux files manually

For example, a reference reading "Figure ?? on page ??" indicates LaTeX could not associate a number with the label. This likely points to a nonexistent label target.

How LaTeX Handles References

To resolve subtle issues, it helps to know how cross-references are processed:

Two LaTeX passes - Labels written to .aux on one pass, read on the next
Out-of-order issues - Later placement can fail reference
\label links to last associated counter
Changes not immediately reflected in references

Correct ordering, multiple compilations, and care when inserting edits can therefore help avoid persistent errors.

Example Code

The following samples demonstrate defining, referring to, and customizing cross-reference labels in LaTeX for common use cases:

Referencing Sections


\section{Introduction} \label{sec:intro}
See the introduction in Section \ref{sec:intro}.

Labels section with descriptive \label command
Section number updates automatically on reference

Linking Figures


\begin{figure}[h]
\centering
  \includegraphics[scale=0.4]{graph.pdf}
  \caption{Results \label{fig:results}}
\end{figure}

The results are shown in Figure \ref{fig:results}.

Figure caption label targets the image
\ref prints the associated "Figure 1.2" number

Reusing Algorithms


\begin{algorithm}
  \caption{Euclid's algorithm \label{alg:euclid}}
  \begin{algorithmic}[1]  
    \Procedure{Euclid}{$a,b$}\Comment{The g.c.d. of a and b}
      \State $r\gets a\bmod b$
      \While{$r\not=0$}
        \State $a\gets b$ 
        \State $b\gets r$
        \State $r\gets a\bmod b$
      \EndWhile\ 
      \State \textbf{return} $b$\Comment{The g.c.d.}
    \EndProcedure
  \end{algorithmic}  
\end{algorithm}

Algorithm \ref{alg:euclid} shows an efficient method to calculate the greatest common divisor.

Labels the full algorithm environment for reference
Link text derives from the algorithm title and label

Live Document Compilation

Test LaTeX cross-referencing features with this interactive online editor: